Folding scaffold



'Sept. 19, 1961 w. J. s. JOHNSON- ET AL 3,000,466

FOLDING SCAFFOLD Filed Dec. 1, 1959 4 Sheets-Sheet 1 INVENTORS:

Wallace J..S.Jo/7nson lZoberf E,F/sher WWW ' ATTORNEYS p 1961 w. J. s.JOHNSON ETAL 3,000,456

FOLDING SCAFFOLD 4 Sheets-Sheet 2 Filed Dec. 1. 1959 INVENTORSI WallaceJ. .S.dohn$on Roberf' E.Ffsher ATTORNEYS Sept. 19, 1961 w. J. s. JOHNSONETAL 3,000,466

FOLDING SCAFFOLD Filed Dec. 1, 1959 4 Sheets-Sheet 3 INVENTORS: WallaceJ. $.d0hnsan BY Qoberf Ef/Zsher WWW ATTORNEYS p 1961 w. J. 5. JOHNSONETAL 3,000,466

FOLDING SCAFFOLD Filed Dec. 1, 1959 4 Sheets-Sheet 4 INVENTORS. WallaceJ. 5. Johnson BY Qoberf E. Fisher ATTORNEYS United States Patent3,000,466 FOLDING SCAFEOLD Wallace J. S. Johnson and Robert E. Fisher,Berkeley, Calif., assignors to Up-Right, Inc, Berkeley, Calif., acorporation of California Y Filed Dec. 1', 1959, Ser. No. 853,041

'10 Claims. (Cl. 182-118) This invention relates to support devices, andmore specifically involves a cross bracing structure for interconnectingspaced vertical support frames and members. It is believed that thisinvention provides a novel folding-bracing principle applicable toperhpas several types of devices but having particular significance inthe construction of scaifolds.

One object of this invention is to provide an improved support structureincluding a cross bracing formed with two pairs of pivotally jointedbracing members and having a disconnectable means for selectivelyjoining their pivoted junctions. i

A second object is to provide a support structure including collapsiblecross bracing of the kind described and having offset connectionspermitting the structure to be compactly folded, yet having no loosebracing members.

A third object of this invention is to provide a support structureincluding disconnectable cross bracing members and having a novel meansfor joining said bracing members into a rigid bracing structure.

Another object is to provide a support structure including a collapsiblecross bracing of the kind describedand having means provided forpreventing uncontrolled spreading of the support and bracing members. i

It is a further object of this invention to provide a one-piececollapsible scaffold structure including spaced vertical support frames,said scaffold having no separte braces or loose parts after its erectionand requiring no tools for its assembly. Such scaffolds as hereindescribed can be erected by one man in a matter of seconds and thesimplicity of the scaffold construction prevents an improper or unsafeassembly.

Still another object is to provide a collapsible scaffold having a pairof spaced vertical supporting frames and including a bracing structurecomprising: a pair of first bracing members pivotally joined together atone end and having opposite ends pivotally joined to respective verticalsupporting frames; a pair of second bracing members pivotally joinedtogether at one end and having opposite ends pivotally joined torespective vertical supporting frames at points above respective firstmember junctions; disconnectable means for selectively joining saidfirst and second bracing members proximate their own pivot junctions; apair of third bracing members pivotally joined together at one end andhaving opposite ends pivotally joined to respective vertical supportingframes; and means for locking said pivotally connected junction of saidthird bracing members into a rigid structure.

Anadditional object of this invention is to provide a collapsiblescaffold having a pair of spaced vertical supporting frames andincluding a bracing structure comprising: a first ladder structurehaving a first pair of spaced bracing members interconnected by steps, asecond pair of spaced bracing members pivotally joined to respectivefirst bracing members, said first and second bracing mebers also beingpivotally joined in pairs to respective vertical supporting frames; asecond ladder structure having a third pair of spaced bracing membersinterconnected by steps, a fourth pair of spaced bracing memberspivotally joined to respective third bracing members, said "ice thirdand fourth bracing members also being pivotally joined in pairs torespective vertical supporting frames and at points above respectivesecond and first member junctions; whereby said first and second ladderstructures complement each other, forming a ladder structure spanningsaid supporting frames.

Other objects and advantages of this invention will become apparent inview of the drawings and the following description.

In the drawings forming a part of this specification, and in which likeparts are designated by like reference numerals throughout the same,

FIG. 1 illustrates a series of elevational views of a collapsible spanscaffold as one embodiment of this invention. FIG. 1a is an endelevation while FIG. 1b and 1c are side elevations, respectively,showing the scaffold in a fully collapsed position and a partiallycollapsed positiOn;

FIG. 2 is a side elevation of the scaifold of FIG. 1 in its initialposition for erection;

FIG. 3 is a side elevation of the scaffold of FIG. 1 in its fullyerected position;

FIG. 4 is a perspective view of the erected scafiold otherwiseillustarted in FIGS. 1 3.

FIG. 5 is the rear elevational view of the disconnectable means emploeydfor joining the cross bracing of the scaffold shown in FIGS. 1-4, thefittings that form the disconnectable means being shown in disconnectedjuxtaposition and prepared for making a locking engagement;

FIG. 6 is a section taken on lines 6-6 of FIG. 5;

FIG. 7 is a perspective view of the disconnectable means shown in FIGS.5 and 6 after the fittings have been mated;

FIG. 8 illustrates two elevational views of a second embodiment ofthis'invention as applied to a ladder scaffolding, :FIG. 8a being an endelevation and FIG. 8b a side elevation, both figures showing thescaffolding in a collapsed or folded position;

FIG. 9 is a perspective view of the ladder scafiolding of FIG. 8 in afully erected position;

FIG. 10 is an elevational view of the disconnectable means employed forjoining the cross bracing of the ladder scafiold, the fittings that formthe disconnectable meaiis being shown in disconnected juxtaposition andprepared for making a locking engagement;

11 is a section taken on lines 1111 of FIG. 10'

I IG. 12 is a perspective view of the disconnectable means shown inFIGS. 10 and 11 after the fittings have been mated;

FIG. 13 is a partial transverse section of the locking pin structureemployed for locking the fittings together;

FIG. 14 is an elevational view of a pivot junction that is utilized forconnecting certain bracing members toits vertical support member;

FIG. 15 is a top plan view of the pivot junction of FIG. 14, taken onlines 15-15 and showing the offset provided;

FIG. 16 is a perspective view of the pivoted link juncture betweenbracing members 28; and

FIG, 17 is an elevational view of a pivoted hook memher on frame 1 14b.

Referring to FIGS. 1-4 of the drawings, there is shown one embodiment ofthis invention as conceived for a collapsible span scaffolding. Thescaffolding generally comprises a pair of spaced ladder support frames10 and 11, each having a pair of vertical support members 12 withhorizontal rung members 13, a frame-connecting bracing structuregenerally designated by reference numeral 14, and a detachable platform15. The structural members are preferably formed from tubular metal suchas aluminum which will provide lightness as well as strength; theplatform can be made from plywood material. If desired, the supportmembers 12 may be provided with casters, as shown, for enabling thescaffolding to be rolled into a designated position. These casters arelocked by manipulation of an operating arm, such a type of caster beingwell known and commonly used in the scalfold art. A clasp arm 101 isalso provided for retaining the scaffold in a folded position. Arm 101is pivotally mounted to a horizontal rung member '13 of one frame anddetachably connects to a member 13 of the opposite frame.

This invention is more particularly characterized by its bracingstructure 14 which includes a first pair of bracing members 16 and asecond pair of bracing members 17, both pairs of bracing members beingpivotally joined in a manner to be more particularly described. Eachpair of bracing members interconnects frames and 11, the ends of saidbracing members being pivotally joined to each frame and said secondbracing members being connected at points above respective first memberconnections. As best shown in FIG. 2, the first and second pairs ofbracing members are interlocked with the other pair, thereby forming aninterlocking V-shaped bracing arrangement. It will be apparent in viewof the drawings that as the side frames 10 and 11 are moved away fromeach other the pairs of bracing members 16 and 17 tend to unfold andtheir respective pivot junctions move toward each other until theyoccupy the erected position, illustrated in FIGS. 3 and 4.

FIGS. 5 and 7 illustrate the manner in which bracing members 16 and 17are pivotally jointed and the means for joining said members together. Apair of mated fittings 18 and 19 is provided at the respective ends of abracing member 16 and a bracing member 17. Each fitting is complementaryto the other, having a receiving pocket 20 and a boss 21. Thus, whenfittings 18 and 19 are brought toward each other in the manner suggestedby the arrows in FIG. 5, the boss and pocket of one fitting will bemoved toward the pocket and boss, respectively of the other fitting.

It will be noted that fittings 18 and 19 are rigidly affixed to but onebracing member, the other member of each pair being pivotally andlaterally connected from each boss portion. As best shown in FIG. 5, thedegree of pivotal movement between boss and pivoted brace member islimited by the engaging contact of a rear fitting surface 22 and thetransverse surface 23 formed at the end of the pivoted brace member. Itwill be understood in view of the drawings that the surfaces 22 and 23only limit the unfolding type movement of each pair of bracing members.Therefore, bracing members 16 can pivot upwardly (and members 17 canpivot downwardly) without limitation or obstruction until they occupy acompletely folded position, as shown by FIG. 1b. The limited pivotalaction, as provided by surfaces 22 and 23, prevents uncontrolledspreading of the bracing members while also establishing a solidconnection between otherwise pivotally joined bracing members when theyare placed into an erected position.

A locking means is also provided adjacent fittings 18 and 19 for holdingthem together once they have been mated. For this purpose a springactuated pinning mechanism 24 is secured to those brace members to whicha fitting is attached. The locking mechanism comprises a pin member 25that transversely pierces its retaining brace member and is springbiased into the path of the fitting on the other brace member. Pin 25 islocated at a point such that when the fittings become completely opposedbrace member and into a locking position, as best known in theperspective view of FIG. 7.

Details of the pinning mechanism 24, divorced from the related fittingstructure, is more particularly shown in FIG. 13. The mechanism, inaddition to pin 25, includes a spring 26 and a clip actuating lever 27,and may be installed as a unit in a tubular bracing member. It will beapparent from the drawings that the clip actuating lever is pivotallymounted to pin 25 and is adapted for folding against the outer surfaceof the brace member as shown in solid line, or may be pivoted to theopposite side of the pin where it operates as a cam for lifting the pininto the broken line position illustrated. Pin 25 is tapered at its end25a to insure a proper locking of the fittings in their mated positionwhile providing an even earlier locking of the parts. Because of thetapered contact between the pin and the rear contact surface on theopposite fitting, the pin will move behind said fittings rear surfacebefore complete mating of the fitting parts. However, as the fittingsare moved closer together a greater pin width emerges from its retainingtubular member thereby maintaining contact with the rear contact surfaceof the fitting. It will be apparent that the taper provided on the pincould as well have been made upon a fittings rear contact surface sinceit is only the relative tapering between the parts that is necessary toproduce the desired effect.

The bracing structure 14 of the scaifold shown in FIGS. 1-4 alsoincludes a pair of cross brace members 28 that are pivotally jointed andinterconnect frames 10 and 11 at pivotally joined ends. The pivotjuncture of members 28, as more particularly shown in FIG. 16, comprisesa link member 29a which is pivotally connected at either end thereof tothe ends of bracing members 28; This pivotal junction enables theaxially aligned bracing members 28 to be pivotally folded together. Alocking sleeve 2% is provided on one bracing member, and this sleeve isadapted to be moved over the pivotal junction mated, the end of said pinwill clear the end of the structurally opposed bracing member. Thespring bias will then cause the pin to be moved behind the end of thewhen the brace members are horizontally aligned, thereby rigidifyingsaid members as a cross brace.

Each of the above described frame connecting pivot junctions is madeupon frame offsets to enable the cross members to be folded intoparallel adjacency. An example of such an offset is more particularlyillustrated in FIG. 14 where member 17 is pivoted upon an axis 30 thatis offset from the frame member 12. The fittings for such an offsetmounting is provided with a cam lobe 31 that is adapted for engaging atransverse surface portion 32 on the brace member. Accordingly, theoutward pivotal movement of brace member 17 is effectively limited tothe position shown, although said member may be freely pivoted intoparallel adjacency with vertical support member 12. Since each of theframe pivot junctions is provided with a similar type pivot connection,it will be understood that the scaffold is not completely free to assumeany position, but that uncontrolled spreading of any one bracing memberis prevented. Also, cam lobes 31 and surface portions 32 are designed tocontact when each brace member is placed into its normally erectedposition. Thus, when the scaffold structure is fully assembled anadditional point of contact is made, rendering the connectionsnon-pivotal and making the structure more rigid.

FIG. 15 illustrates the particular ofiset arrangement provided atdiagonally opposite frame pivot junctions of a bracing member 16 and abracing member 17. This ofiset structure is inserted to place diagonallyopposite members in a common bracing plane, thereby accommodating thecooperation between fittings 18 and 19. The other member 16 and itsopposing member 17 are also disposed for pivoting in a common plane byreason that different from each other pair member but in a plane commonto the diagonallyopposed bracing member of the other pair. Thisrelationship of members insures a proper actuation of the bracingstructure for effecting a proper mating of fittings 18 and 191 Withscaffold structures as above described and shown in the drawings, afolded scaffold unit may be assembled by separating frames and 11 in themanner illustrated in FIGS. 1 and 2. Where one-man operation is employedthe vertical members 12 are initially allowed toincline inwardly,thereby maintaining a controlled balance of the structure while thecross brace 28 is straightened and made rigidf With the locking ofsleeve 29b across the pivotedlink junction of members 28, theintermediate pivot junctions of members 16 and 17 will be proximate oneanother. The operator .will, then, by grasping two diagonally oppositemembers 16' and 17 move their respective pivot fittings 18 and 19 towardthe other. The pins 25 of each locking mechanism 24 will engage theinclined surface of the diagonally opposite bracing member and becarnmed into a retracted position. Then, by moving the fittings towardoneanother and putting them into a mated position, pins 25 will emergefrom behind the diagonally opposite member, locking the fittingstogether. In this condition and position 'of bracing members, each ofthe fittings pivot junctions is rigidified by contact of surfaces 22 and23, and the'frame pivot junctions' are each rigidified by contact ofsurfaces 31 and 32.

The spacing between frames 12 is of course established by the lengths ofthe bracing members. But by proportioning the lengths of cross bracemembers 28 to the lengths of cross brace members 16 and 17, the bracingaxis of each member 16 will be substantially parallel with the axis ofits diagonally opposite member 17. This provides an almost continuoussupport axis between the frames and the torsional forces applied to thefittings 18 and 19.

It will be further noted that pivotally joined bracing members are ofequal length from their common pivot axis to the support pivot axes uponthe frames, and that the common pivot axes of both pairs of bracingmembers are vertically aligned. This will be an essential condition fora collapsible scaffold which can be compactly folded as shown in FIG.16. Since horizontal members 28 also form a part of this collapsiblestructure, the distance between a link pivot connection and the framepivot axis for the joined member is the same for both members.

FIGS. 8-12 illustrate a second embodiment of this invention as appliedto a stairway scaffold. In broad terms of inclusion, the stairwayscaffold comprises support frames 110 and 111 having vertical supportmembers 112 and horizontal ties 113 and cross bracing means 114,including stairway cross bracing 114a and a horizontal platform supportframe 11412. As with the previously described scaffold structure,casters and clasp arms 101 may be provided.

The stairway cross bracing 114a comprises four pairs of parallel bracingmembers 116, 117, 118, and 119, each pair connecting to a horizontal tie113 upon a pivotal junction that is oifset between the frames, therebyper-' mitting compact folding. Bracing members 116 are pivotally joinedto members 119, and members 117 are pivotally connected to members 118,each pair of pivotally joined members 116 and 119 being pivotallyinterlocked with a pair of pivotally joined members 117 and 118. Aplurality of steps 120 is provided across members 116 and 118 therebyforming ladder structures, which, when the scaffold is assembled asillustrated in FIG. 9, provides a continuous stairway spanning frames110 and 111.

The pivotal connections between bracing members are made with fittingssimilar to that described for the previous embodiment. However, it willbe noted that the pivotally joined bracing members 116 through 119 areshorter in length than the vertical distance between the two horizontaltie members 113 of each frame from which they are supported. Thus, whenth scattold is foldedthe fittings take a position between the supportingpivot junctions provided upon the tie members 113. If fittingsillustrated in FIG. 5- were'used, portions of the fittings 18 and 19,-Which define pockets 20, w lie in the pivot plane of one bracing memberand p even-t complete folding of the scafiold. Accordingly, clearancehas been provided upon each fitting such that there will be nointerference between fittings and bracing members. This. clearance k shae f h cross. brace filfil somewhat different from those previouslydescrib d.

Referring more particularly to FIGS. 10-12, there is shown a pair ofmated fittings .121 and 122 which may be used for the ladder scaffold ofFIGS. 8 and 9,. Two pairs of these fittings will of course be necessary,one for each four bracing members on both sides of the ladder struc:ture. Fittings 121 and 122 are rigidly afiixed to one bracing member andhave another member pivotally and laterally connected thereto. Eachfitting is complemen: tary to the other, having a stop member 123 and aboss .124. When the fittings are moved toward one another, the boss ofone engages a lip edge 125 provided by the back edge of the others stopmember. It will be noted that the lip edges limit relative movement ofthe fittings, but being less pronounced than the pocket surface offittings 18 and 19, they provide clearance for members 116 and 118, whenupon folding the scaffold, said members are respectively pivoted intoalignment with members 117 and 119. Such a clearance was unnecessary inthe previously described structure since the fittings 18 and 19 extendedabove or below the frame pivot junctions of the opposite members.

The degree of pivotal movement between a fitting and a pivoted bracemember is limited by the engagement of a rear fitting surface 126 and abrace member surface 127 in the same manner and for reasons previouslygiven in describing the fittings 18 and 19. Also, each pair of fittingsis provided with a locking mechanism 24- which operates identically tothose devices provided with fittings 18 and 19. While two lockingmechanisms were provided for each pair of fittings in the other scaffoldstructure, only one such mechanism is used per pair of fittings 121 and122 since this allows a single person to operate both pairs of fittingssimultaneously.

Horizontal platform support frame 114b is pivotally connected at offsetjunctions 128 in the same manner as for the stairway cross bracing 114a.The opposite end of support frame 114]) has a pair of hook members 129,that are pivoted to the frame 11 4b (FIG. 17) and are therefore adaptedto be pivoted over tie 113 after frames and 111 are spread and frame114b is raised to the proximate level of tie 113.

To operate the ladder scaffolding into an assembled position asillustrated in FIG. 9, it is only necessary to separate the frames 110and 111 in the manner described for the span scaffolding of FIGS. 1-4.The horizontal support structure 114b is, however, positionedsubsequently to the erection of cross bracing 114a. Fittings 121 and 122connect in precisely the same fashion as fittings 18 and 19, eachpinning mechanism dropping'behind the end surface of the oppositefitting as the fittings are mated.

It will be noted from the (folded side view, FIG. 811, that the scaifoldframes 110 and 111 are of unequal height. The reason for this is thatthe scaffolding is designed to receive standard scaffolding unit ofother construction on top. Of course, an upper tier scaffolding havingthe novel ladder bracing structure embodied in the illustrated groundsupport section is contemplated, and in such case the leg members whichsupplement vertical supports 112 on frame 111 will be longer than thoseleg members mating with supports 112 on frame 110. Since additionaltiers of scaffolding will be initially 7 braced into a spread positionby the vertical supports 112 of the lower tier, it is possible to omitpinning mechanisms from the fittings of upper tiers.

It will be apparent in view of the above disclosure and the drawingsthat there has been provided a novel improvement in support structuresas well as scaffolding constructions. While several embodiments of thisinvention are shown and described, it is to be understood that variouschanges in the shape, size and arrangement of certain parts may beresorted to without departing from the'spir'it of the invention or thescope of the attached claims, and each of those changes is contemplated.

Having thus described our invention, what We claim and desire to secureby Letters Patent is:

1. In a support structure having a pair of spaced vertical supportmembers, first and second pairs of first and second bracing memberspivotally interconnecting said spaced support members, and theimprovement comprising: a pair of mated fittings, said fittings beingrigidly attached to the end of a first bracing member and pivotallyjoined to the end of a second bracing mem ber, each fitting having firstand second surfaces thereon extending substantially transversely to theaxis of said first bracing member and being axially located for beingengaged by corresponding second and first surfaces, respectively, ofsaid other fitting when said fittings are mated.

2.. The support structure and improvement of claim 1 including a meansfor locking said fittings in an engaged position.

3. The support structure and improvement of claim 1 wherein each fittingprovides means for limiting pivotal movement of said second bracingmember to establish a predetermined angle between axes of first andsecond bracing members when said fittings are mated, causing saidbracing members to be rigidified.

4. A support structure having a pair of spaced vertical support membersand including a bracing means therebetween comprising: first and secondpairs of first and second bracing members, the bracing members of eachpair being pivotally connected at one of their ends to said supportmembers, a pair of mated fittings, said fittings being rigidly attachedto the end of a first bracing member and pivotally joined to the end ofa corresponding second bracing member, each fitting having first andsecond surfaces thereon extending substantially transversely to the axisof said first bracing member and being axially located for being engagedby the second and first surfaces, respectively, of said other fittingwhen said fittings are mated, a third surface provided on one of saidfittings and extending substantially transversely to the axis of thefirst bracing member to which said one fitting is attached, and alocking pin reciprocally mounted in the first bracing member to whichsaid other fitting is attached, said locking pin being engagab le withsaid third surface when said fittings are mated.

5. The support structure of claim 4 wherein each fitting provides meansfor limiting pivotal movement of said second bracing member to establisha predetermined angle between axes of first and second bracing memberswhen said fittings are mated, causing said pairs of bracing members tobe rigidified.

6. A collapsible scaffold having a pair of spaced vertical supportingframes and including a bracing structure comprising: a first ladderstructure having a first pair of spaced bracing members interconnectedby steps, a second pair of spaced bracing members pivotally joined torespective first bracing members, said first and second bracing membersalso being pivotally joined in pairs to respective vertical supportingframes; a second ladder structure having a third pair of spaced bracingmembers interconnected by steps, a fourth pair of spaced bracing memberspivotally joined to respective third bracing members, said third andfourth bracing members also being pivotally joined in pairs torespective vertical supporting frames and at points above respectivesecond and first member junctions; said first and second pairs ofbracing members being interlocked with said third and fourth pairs ofbracing members; whereby said first and second ladder structurescomplement each other, forming a ladder structure spanning saidsupporting frames.

7. A collapsible scaffold having a pair of spaced verti cal supportingframes and including a bracing structure comprising: a first ladderstructure having a first pair of spaced bracing members interconnectedby steps, a second pair of spaced bracing members pivotally joined torespective first bracing members, said first and second bracing membersalso being pivotally joined in pairs to respective vertical supportingframes; a second ladder structure having a third pair of spaced bracingmembers interconnected by steps, a fourth pair of spaced bracing memberspivotally joined to respective third bracing members, said third andfourth bracing members also being pivotally joined in pairs torespective vertical supporting frames and at points above respectivesecond and first member junctions; said first and second pairs ofbracing members being interlocked with said third and fourth pairs ofbracing members; and means provided adjacent each of said pivotjunctions between bracing members for limiting pivotal movement of eachbracing member with respect to a pivotally joined bracing member to aposition of erection, thereby preventing uncontrolled spreading of saidbracing members while providing a rigid connection when said scaffold iserected; whereby said first and second ladder structures comple menteach other, forming a ladder structure spanning said supporting frames.

8. The scaffold structure of claim 7 wherein each bracing member ispivotally mounted to said support frames upon offsets between saidframes, allowing said bracing members to be pivoted toward saidsupporting frames into parallel adjacency therewith.

9. A collapsible scaffold having a pair of spaced vertical supportingframes and including a bracing structure comprising: a first ladderstructure having a first pair of spaced bracing members interconnectedby steps, a second pair of spaced bracing members pivotally joined torespective first bracing members, said first and second bracing membersalso being pivotally joined in pairs to respective vertical supportingframes; a second ladder structure having a third pair of spaced bracingmembers interconnected by steps, a fourth pair of spaced bracing memberspivotally joined to respective third bracing members, said third andfourth bracing members also being pivotally joined in pairs torespective vertical supporting frames and at points above respectivesecond and first member junctions; said first and second pairs ofbracing members being interlocked with said third and fourth pairs ofbracing members; first and second pairs of mated fittings, one fittingof each pair interconnecting a first and a second bracing member, theother fitting of each pair interconnecting the corresponding third andfourth bracing members; each fitting of said pairs having first andsecond surfaces thereon extending substantially transversely to the axisof one bracing member and being axially located for being engaged bycorresponding second first surfaces, respectively, of the other fittingof said pair when said fittings are mated.

10. A collapsible scaffold having a pair of spaced vertical supportingframes and including a bracing structure comprising: a first ladderstructure having a first pair of spaced bracing members interconnectedby steps, a second pair of spaced bracing members pivotally joined torespective first bracing members, said first and second bracing membersalso being pivotally joined in pairs to respective vertical supportingframes; a second ladder structure having a third pair of spaced bracingmembers interconnected by steps, a fourth pair of spaced bracing memberspivotally joined to respective third bracing 9 members, said third andfourth bracing members also being pivotally joined in pairs torespective vertical supporting frames and at points above respectivesecond and first member junctions; said first and second pairs ofbracing members being interlocked with said third and fourth pairs ofbracing members; a rigid horizontal support member interconnecting saidframes and having one end pivotally connected to one frame anddetachably connected to the other frame; whereby said first and secondladder structures complement each other, forming a ladder structurespanning said supporting frames.

References Cited in the file of this patent UNITED STATES PATENTS RitterNov. 29, Miller Dec. 25, Johnson et a1 Mar. 23, Bobst Jan. 12, HofheimerAug. 16, Sheard May 8, Mulder Mar. 4, De Palma Dec. 15, Kowalski Dec.27,

